With it saying "Winter Soldier" right there in the title, I'm sure they're not going to try to go all M. Night Shamalamadingdong and try to save his identity for a "SHOCKING PLOT TWIST!!!" I figure they'll introduce WS first as the hit-man on ice, then have Cap start investigating him early in the movie, and probably discover that it's really Bucky by the end of Act I, say 20-30 minutes in. The middle of the movie will likely deal with Cap trying to break through to Bucky and reprogram him, just in time for them to team up against Zemo (or whoever) in the third reel.

Agreed. I think the suspense will come more from expectation of what'll happen when Steve finds out, rather than a driving question being 'Who is the Winter Soldier?'